Sequential,fixed-bed hydrodesulfurization system

ABSTRACT

AN APPARTUS FOR THE HYDRODESULFURIZATION OF SULFURCONTAINING HYDROCARBONS WHERIN THE HYDROCARBON IS REACTED IN A FIRST STAGE WITH HYDROGEN IN THE PRESENCE OF A HYDROGEN TRANSFER CATALYST TO PRODUCE H2S, AND WHEREIN THE H2S SO PRODUCED IS REACTED WITH AN ALKALINE MATERIAL IN A SECOND STAGE TO PRODUCE A SOLID PHASE SULFIDE BEFORE IT CAN COMBINE WITH THE DESULFURIZED HYDROCARBONS. THE INVENTION IS PARTICULARLY USEFUL IN HYDRODESULFURIZING ASPHALTIC AND REDUCED CRUDES. A SERIES OF THE AFOREMENTIONED STAGES MAY BE LINKED TOGETHER TO FORM AN EFFICIENT HYDRODESULFURIZATION SYSTEM.

Desu/fur/zed Producf Hydrogen Gas BY ATTORNEY A. N. WENNERBERG Filed Aug. 15, 1968 Recycle Hydrogen Gas 6 0 N TA 0 TO I? S SEQUENTIAL, FIXED-BED HYDRODESULFURIZATION SYSTEM Aug. 10, 1971 Hydrocarbon Feed l9 United States Patent 01 ifice 3,598,535 Patented Aug. 10, T971 U.S. Cl. 23-260 Claims ABSTRACT OF THE DISCLOSURE An apparatus for the hydrodesulfurization of sulfurcontaining hydrocarbons wherein the hydrocarbon is reacted in a first stage with hydrogen in the presence of a hydrogen transfer catalyst to produce H 8, and wherein the H 8 so produced is reacted with an alkaline material in a second stage to produce a solid phase sulfide before it can combine with the desulfurized hydrocarbons. The invention is particularly useful in hydrodesulfurizing asphaltic and reduced crudes. A series of the aforementioned stages may be linked together to form an efiicient hydrodesulfurization system.

BACKGROUND OF THE INVENTION It is well known that the removal of sulfur from petroleum is of great importance to refiners. In the United States alone, nearly twelve million dollars are spent yearly on research and development in finding Ways of desulfurizing petroleum stocks. As sources of high grade crude oil become depleted, it is necessary to process greater quantities of high sulfur crudes in order to meet the ever increasing demand for petroleum products. This fact, coupled with the growing concern of the public with respect to air pollution, clearly points out that refiners must develop improved commercial methods for eliminating sulfur from crude oil and from petroleum products.

Sulfur is present in petroleumin many forms. It may appear as mercaptans, sulfides, disulfides, and complex ring compounds such as thiophenes. The presence of sulfur in gasoline requires using larger quantities of expensive antiknock compounds in the gasoline to meet the needs of modern high-compression internal combustion engines. This fact provides an economic incentive to eliminate or at least to substantially reduce the level of sulfur in gasoline. Furthermore, motor fuels containing sulfur generally have disagreeable odors and tend to have undesirable gum-forming characteristics. When sulfurcontaining fuel oils are burned, the combined sulfur is oxidized to sulfur dioxide, which is a major pollutant of air.

As a result of research, many desulfurization processes have been developed and are now available. It has been found that the removal of sulfur from low boiling petroleum fractions is not difficult but that as the boiling point increases, the difliculty of desulfurization likewise increases. Similarly, it is generally more difiicult to desulfurize a naphthenic molecule than a paraflinic molecule, and still more diflicult to desulfurize an aromatic molecule. Consequently, although suitable desulfurization methods are available for use with light and intermediate petroleum stocks, an improved hydrodesulfurization process is needed for treating the heavier petroleum stocks.

In my copending application, S.N. 758,752 being filed concurrently herewith, I have disclosed a fundamentally new process for desulfurizing hydrocarbons. The method involves the desulfurization of hydrocarbons in the presence of hydrogen gas, a hydrogen donor and/or a hydrogen transfer catalyst, and a strong alkaline reactant.

In the present application, I disclose an apparatus for practically applying some of the broad teachings of the aforesaid patent application in order to provide a commercially feasible hydrodesulfurization system. Using the apparatus of the instant invention, it is possible to maintain continuous hydrodesulfurization with blocked out base regeneration for continuous H S scrubbing. This invention provides not only the basic element of continuous operation for a hydrodesulfurization process but, in certain embodiments, provides invaluable flexibility in operation for developmental studies.

SUMMARY OF THE INVENTION My invention broadly relates to the hydrodesulfurization and upgrading of petroleum stocks which contain combined sulfur. It is particularly adaptable for the de sulfurization of heavy asphaltic crude oils and residual stocks. In particular, my invention relates to an apparatus for hydrodesulfurizing a sulfur-containing hydrocarbons wherein the hydrocarbon feed is treated alternately in a hydrodesulfurization zone and then in an alkaline or base contacting zone; The apparatus used employs a fixed-bed design and embodies an operating sequence to provide the necessary base capacity to react with product H S, thereby minimizing catalyzed recombination reactants of H 8 and other forms of free sulfur with sulfur-free product hydrocarbons. At the same time it provides for continuous regeneration of the alkaline system with possible recovery of sulfur and/or H S, depending upon the alkaline reactant selected.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic flow diagram of a preferred embodiment of my improved hydrodesulfurization apparatus showing three reactor-contactor pairs, a gas separator vessel, and fractionator.

DETAILED DESCRIPTION AND EMBODIMENTS In conventional hydrodesulfurization processes, the sulfur-containing hydrocarbon is contacted with hydrogen gas at elevated temperatures and pressures in the presence of a hydrogen transfer catalyst so that the sulfur is sprung from the hydrocarbon molecule and combines with the hydrogen gas to form H 3. Unfortunately, if the hydrogen sulfide remains in the presence of the hydrocarbon molecule secondary recombination reactions can take place resulting in resulfurization of the hydrocarbon. However, this recombination can be avoided by reacting the H 8 with another material before it can react with the hydrocarbon. Accordingly, I have found that the aforesaid may be accomplished by passing the hydrocarbon, unreacted hydrogen, and evolved H 8 from a conventional hydrodesulfurization zone into a contacting 'zone containing a base or alkaline reactant composition at such conditions of temperature and pressure that the H 5 reacts with the alkaline composition to form a solid phase sulfide.

Because it is desirable to avoid the recombination of the H 8 with the hydrocarbon, it may be advantageous to limit the extent of hydrodesulfurization and resultant H S concentration in each particular zone under relatively mild conditions in which not all of the combined sulfur is removed from the hydrocarbon before it is passed into the alkaline contacting zone. This avoids the production of large concentrations of H 8. Operation in this manner necessitates having a plurality of hydrodesulfurization zones, each one followed by an alkaline contacting zone. The hydrodesulfurization zone operating conditions depend upon the hydrocarbon feed composition, the sulfur content of the feed, the manner in which the sulfur is combined with the feed, the degree of desulfurization desired, and the operating conditions of the various zones.

It is clear that the hydrodesulfurization zone and alkaline contacting zone need not all have the same operating conditions and it is equally clear that all zones of the same type need not have the same operating conditions. It would be preferable that is a series of hydrodesulfurization-alkaline contacting zone pairs, the down-stream hydrodesulfurization zones be operated at more severe conditions than the up-stream zones. This, of course, is because it becomes progressively more difficult to remove the last of the combined sulfur. The apparatus of my invention is ideally suited for flexibility in adjusting the operating conditions throughout the hydrodesulfurization system.

Any base composition which will react with H S to form a solid phase sulfide may be used in the contactor. Ideally, the alkaline reactant composition will not substantially react with the hydrocarbon material or the hydrogen gas present at the conditions of temperature and pressure within the contacting zone. Suitable base compositions for use with the method and apparatus of my invention may be selected from the group consisting of the oxides, hydrated oxides, and sulfides of the alkaline earth elements. Similarly, the base compositions may be selected from the group consisting of the hydroxides, oxides, and sulfides of alkali metals. It is contemplated that the base compositions may comprise mixtures of the aforementioned compounds. It is also contemplated that these compositions may be present either alone in the contacting zone or may be absorbed on a suitable support to form one or more fixed beds of contacting within a reactor.

While the exact temperature and pressure Within the contacting zone is a function of many variables including the composition and sulfur concentrations of the gas stream and the nature of the alkaline contacting compositions, it has been found that a temperature of between about 700 and 800 F., preferably 750800 F. and a pressure between about 700 p.s.i.g. and 2,000 p.s.i.g., preferably from about 1,000 p.s.i.g. to 1,200 p.s.i.g. are satisfactory.

The apparatus of my invention comprises a plurality of hydrodesulfurization reactor-base composition contactor pairs. The reactors each contain at least one fixed bed comprising a conventional acid-type hydrodesulfurization catalyst or an alkalized hydrogenation-hydrodesulfurization catalyst. Suitable catalysts for use in the hydrodesulfurization reactors are: CoO.MoO .Al O MoO .Al O Wo .Al O NiO.MoO .Al O Each of the contactors contains at least one fixed bed comprising a base composition suitable for tying up the H 8 evolved in the hydrodesulfurization reactors. Suitable compositions were described above.

The reactor-contactor pairs are connected so that efiiuent from a reactor passes to the inlet of a contactor. Although a single reactor-contactor pair may be adequate for the hydrodesulfurization of some materials, it is preferred to have a pluarlity of these reactor-contactor pairs arranged in series to provide increased desulfurization capabilities of the system.

Each of the reactors may be provided with a hydrogen gas inlet so that fresh hydrogen may be continuously introduced into the system. It is also within the scope of my invention to provide more than one contactor for each reactor. In such an embodiment the contactors would be connected to each other in parallel so that eflluent from a reactor could either pass into all of the contactors associated with the reactor or, alternatively only into some of the contactors so connected. The contactor or contactors not receiving reactor eflluent could then be having the base composition either regenerated or replaced.

In another embodiment, the reactor-contactor pair may also be arranged in series with a by-pass connection provided around each reactor-contactor pair within the series. The purpose of the by-pass contactor is to permit any one or more of the reactor-contactor pairs to be by-passed for catalyst regeneration, repair, or maintenance while permitting the rest of the hydrodesulfurization system to remain operative. Of course the contactors associated with the by-passed reactor may also have base composition regenerated While the by-passed reactor is shut down. Another embodiment involves having a plurality of reactors connected in parallel and associated with one or more contactors connected in parallel to provide an even more flexible system.

In order to provide a complete and operational hydrodesulfurization system, the outlet of the last contactor in the series should connect to a gas separator-pressure let down vessel in which hydrogen gas is separated from the desulfurized product. The hydrogen gas can either be purged or recycled to one of the reactors in the series. Should it be desirable to recycle selected boiling range fractions of the hydrocarbon in order to take advantage of hydrogen donor properties of product hydrocarbons, or to rehydrogenate the more difiicultly desulfurized components, a fractionation system may be adapted to receive the desulfurized product from the gas separator-pressure let down vessel. Certain portions of the desulfurized product may then be recycled from the fractionated system back to one of the reactors in the reactor-contactor series.

It is understood that the hydrocarbon feed to the hydrodesulfurization system may also contain various nitrogenous components. In the apparatus of my invention these nitrogenous components will be hydrogenated to ammonia gas and this gas may be effectively scrubbed out of the system. Provisions for the rapid removal of the ammonia gas can be made by scrubbing the ammonia from the hydrogen recycle stream and/or the degassed product stream.

An important feature of this apparatus is that the base composition in the fixed-bed contactors are capable of regeneration when necessary. After prologned usage, the base will eventually be unable to effectively tie up the H S product. It then becomes necessary either to replace the spent base composition or to regenerate it by treatment with steam at high temperatures, preferably in the presence of carbon dioxide or hydrogen gas.

Referring now to the drawing of a preferred embodiment of my invention, fixed-bed hydrodesulfurization reactor 10 is connected to fixed-bed alkaline contactors 11a and 1112 which are connected in parallel to provide a flow path from reactor 10 directly to contactors 11a and 1112. Likewise, fixed-bed hydrodesulfurization reactor 12 is connected to fixed-bed alkaline contactors 13a and 13b. Contactors 11a and 11b are connected to reactor 12 to provide a direct flow path from contactors 11a ad 11b to reactor 12. Similarly, contactors 13a and 131) are connected to reactor 14. The outlets of contactors 15a and 15b are connected to gas separator-presssure let down vessel 16 to provide a direct path from contactors 15a and 15b to vessel 16. Vessel 16 connects to fractionating system 17 from which desulfurized product is removed at outlet 18.

Hydrocarbon feed from source 19 and hydrogen gas from source 20 are merged in manifold 21 and flow into reactor 10 through valve 22. If desired, the mixture of hydrocarbon feed and hydrogen gas may be bypassed around reactor 10 and contactors 11a and 11b through bypass valve 23 to permit flow into bypass line 24. Effluent from reactor 10 passes via outlet line 25 to contactors 11a and 1117 via valved lines 26a and 26b. Normally, flow will be only to one of parallel contactors 11a or 1111 since the other contactor will be undergoing regeneration. Connections of contactors 11a and 11b to steam and either hydrogen or carbon dioxide facilities for regeneration of the alkaline material are not shown on the drawing. Efliuent from contactors 11a and 111; exit via valved lines 27a and 27b to line 28. From line 28 the eifiuent material may pass into reactor 12 via valve 29 or, alternatively, may be bypassed around reactor 12 and contactors 13a and 13b by flowing into line 24 via valve 30. Note that if the hydrogen and hydrocarbon feed mixture is bypassed around reactor and contactors 11a and 11b, the mixture could then enter reactor 12 from line 24 via valve and valve 29.

In a similar manner, material from reactor 12 flows to contactors 13a and 13b via outlet line 31 and valved lines 32a and 32b. Eflluent from contactors 13a and 13b exit via valved lines 33a and 33b to line 34. From line 34, the material can flow into reactor 14 via valve 35 or, alternatively, it can be passed around reactor 14 and contactors 15a and 15b by flowing into line 24 via valve 36. Once again, it should be noted that material that is bypassed around reactor 12 and contactors 13a and 13b can enter reactor 14 from line 24 via valve 36 and valve 35.

Similarly, material from reactor 14 flows to contactor 15a and/or 15b via outlet line 37 and valved lines 38a and 38b. The material exits from contactors 15a and 15b via valved lines 39a and 39b and passes to gas separator-pressure let down vessel 16 via line 40. Any material bypassed around reactor 14 and contactors 15a and 15b can flow from line 24 to line 40 via valve 41.

In vessel 16, hydrogen gas is separated from the hydrocarbon material and is then recycled to manifold 21 via valved line 42. The desulfurized hydrocarbon passes to fractionating system 17 via line 43. In fractionating system 17, a lower boiling fraction is taken off as desulfurized product from outlet 18 and a higher boiling fraction is recycled to one of the hydrosulfurization reactors via line 44 and any one of valved lines 45, 46 or 47.

The hydrogen gas flow in the described system should be from about 300 to about 2,000 s.c.f./barrel of feed, depending upon the sulfur level in the feed. The feed liquid hourly space velocity (based on the catalyst or the alkaline material) would be between about 0.2 and 2.0 depending on the feed stock and the sulfur level in the feed. For the desulfurization and heavy residue and asphaltic materials, liquid hourly space velocities in the range of 0.2 to 0.4 would be required.

Having thus described my invention, what I claim is:

1. An apparatus for desulfurizing sulfur-containing hydrocarbons in the presence of hydrogen, comprising:

(a) a plurality of fixed-bed reactors, one of said reactors being a lead reactor, each containing at least one catalyst bed comprising a hydrodesulfurization catalyst, each reactor having an inlet means on one side of the catalyst bed and an outlet means on the other side of the catalyst bed;

(b) a plurality of contactor 'banks, one of said contactor banks being a tail contactor bank, each contactor bank being associated with one of said reactors to form a reactor-contactor bank pair, each contactor bank including:

at least two contactors, each of which contains at least one fixed-bed contacting zone comprising an alkaline composition, and each contactor having an inlet on one side of said contacting zone and an outlet on the other side of said contacting zone;

inlet manifold means having an inlet end and a plurality of outlet ends, each of said outlet ends being connected to an inlet of a contactor of said contactor bank;

outlet manifold means having an outlet end and a plurality of inlet ends, each of said inlet ends being connected to an outlet of a contactor of said contactor bank to permit parallel flow through the contactors of a contacting bank; and

interrupting means whereby flow to and through each contactor of a contactor bank can be prevented;

(c) separator means connected to the outlet of the tail contactor bank outlet manifold and in fluid communication therewith, said separating means having a gas stream outlet and a liquid stream outlet;

((1) feed means connected to the inlet means of the lead reactor and in fluid communication therewith for the introduction of hydrocarbons and hydrogen into said lead reactor; and

(e) connecting conduit connecting said reactors and said contactor banks alternatively in series, said conduit commencing at the outlet means of the lead reactor and terminating at the inlet end of the inlet manifold of the tail contactor bank, said conduit con necting the outlet means of a reactor with the inlet end of the inlet manifold of a contactor bank, and connecting the outlet end of the outlet manifold of a contactor bank with the inlet means of a reactor, to permit flow from said feed means through each of said reactor-contactor bank pairs to said separator means.

2. The apparatus of claim 1 wherein said alkaline composition is selected from the group consisting of the oxides, oxide-carbonates, hydrated oxides, and sulfides of the alkaline earth metals, and mixtures thereof.

3. The apparatus of claim 1 wherein said alkaline composition is selected from the group consisting of the oxides, hydroxides and sulfides of the alkali metals, and mixtures thereof.

4. The apparatus of claim 1 wherein each reactor is provided with a valved bypass conduit in order to permit flow around said reactor.

5. The apparatus of claim 1 wherein each contactor bank is provided with a valved bypass conduit in order to permit flow around said contactor bank.

6. The apparatus of claim 1, wherein each reactorcontactor bank pair is provided with a valved bypass conduit, said conduit extending from the inlet of the reactor of said pair to the outlet manifold of the contactor bank of said pair to permit flow around said reactor-contactor bank pair.

7. The apparatus of claim 1 further including a fractionator means, said fractionator means connected to and in fluid communication with the liquid outlet of said separator, said fractionator capable of separating a hydrocarbon into a high-boiling stream and a low-boiling stream and said fractionator connected to said feed means wherein at least a portion of said high-boiling stream is recycled to said feed means and wherein the gas stream outlet of said separator is connected to and in fluid communication with said feed means.

8. The apparatus of claim 4 wherein each reactor is provided with a catalyst regeneration means to permit regeneration of said hydrodesulfurization catalyst when hydrocarbons are not passing through said reactor.

9. The apparatus of claim 1 wherein each contactor of each contactor bank is provided with regeneration means to regeneratet he alkaline composition when hydrocarbon and H S are not entering said contactor.

10. The apparatus of claim 6 wherein each reactor is provided with a catalyst regeneration means and each contactor bank is provided with an alkaline composition regenertion means so that the catalyst and the alkaline composition can be regenerated when hydrocarbon is bypassed around said reactor-contactor bank pair.

References Cited UNITED STATES PATENTS 2,363,716 11/1944 Wolk 28288 2,415,197 2/1947 Van Peski 260-68367 2,845,382 7/1958 Leum et a1 208-226 3,392,002 7/1968 Hamilton, J12, et 'al. 23263 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner US. Cl. X.R. 

